In Java EE applications you are safe to consider that every method in a session bean has an associated transaction, since there is an implicit declaration of the transaction attribute required. If you like to change this behavior you have to configure this proactively by adding the annotation @TransactionAttribute with another value (see enum TransactionAttributeType). Context and Dependency Injection (CDI) does not have such an implicit declaration and no direct container managed support for transactions. But it has a very nice realization of the interceptor concept. This post shows, how to facilitate an interceptor in order to add a transaction to every (or a selection) method in a CDI bean, if it does not already exist. This is the default behavior of required.
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Circumvent Nested Transaction Issues in Tapestry-5.x
Ajax component events may be wrapped in a transaction as I pointed out in “Transaction Handling for Ajax Components in Tapestry-5.x“. But on some occasions an Ajax component event is surrounded by a component event. So the code in the ControllerUtil of article “Transaction Handling in Tapestry5” will lead to ‘transaction already active’ problems, since we try to begin a transaction in the nested ajax component event although there is already an active transaction attached to the current thread. We can overcome this situation by checking, whether an active transaction is present and begin/commit/rollback a new transaction iff not. This behavior is similar to the default transaction attribute REQUIRED in Java EE.
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Transaction Handling for Ajax Components in Tapestry-5.x
In “Transaction Handling in Tapestry5” I described, how to configure transactions wrapping a complete page or component render request. The same is necessary (possible) for Ajax components. Besides having less transactions and sharing the first-level-cache for subsequent calls, this realizes the “Open Session in View Pattern” automatically. So you can access the database lazily via getter from an entity, for example, without running into lazy loading exceptions due to the fact that the transaction has been closed and the entities are detached already.
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Inject Java EE Beans into Tapestry-5.x
Tapestry uses it’s own Inversion Of Control (IOC) container. Tapestry pages are not Servlets or Servlet Filter (and not another managed class). Therefore they cannot be used for injection of Java EE Beans. But there is the AppModule, which is conceptual some kind of related to Spring Java Config. It allows to configure the Tapestry application directly in Java. Like everything in Tapestry it has an Adaptive API. Hence you have to follow a naming (signature) pattern for your methods and Tapestry finds them. You don’t have to implement an interface.
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Tapestry-5.3.1 and Jboss-7.0.2-Final
The Java web framework Tapestry 5 has a hot deployment/reload feature, that traverses the classpath, looking for new resources to load. Unfortunately, it is not capable to parse URLs of Jboss’ virtual file system and therefore does not find it’s own core libraries. This issue has been tracked in TAP5-576 and a solution for Jboss-5 and Jboss-6 can be found in the corresponding wiki articles. The same problem remains for Jboss-7. Accidentally the reflective calls to virtual file are restricted. But the solution for Jboss-6.1 does still work. Here is a little tutorial how to achieve this.
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Concurrent conversion of SVG to formats like PNG, EPS or PDF
In this post I’ll show how to use the ExecutorService of the java.concurrent package, in order to start as many inkscape shells as processors available on the current machine and to distribute a whole bunch of conversion tasks wisely on the cores. On my quad core I got a speedup of about 3.5, which is really near to 4.
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Informative Exceptions with Java Proxies
Information is essential for reasonable exception handling. Unfortunately, it is not always affordable to write custom exceptions providing all necessary information, especially in test code, e.g. for selenium tests. So, here is an approach to weave informative exceptions into your [test] code.
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Circular Dependencies of Session Beans via Manual EJB Lookup
In my last two posts (Circular Dependencies of Session Beans and Circular injection of Util Classes in EJB 3.0) I wrote, that it is possible to have circular dependencies between session beans via interceptors and manual EJB lookup. In this post I will sketch out how.
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Circular Injection of Util Classes in EJB 3.0
In my last post Circular Dependencies of Session Beans I presented a method to use interceptors in session beans in order to inject beans. This works great until you want to add circular dependencies. Then you have to look up the beans by name and inject them into the bean. But this is kind of cumbersome. So, if it is possible, have a bean structure, which is topologically sortable and inject util classes having circular dependencies between each other. This post shows how to achieve the latter.
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Circular Dependencies of Session Beans
This post is about circular dependencies between session beans (ejb 3.0), which is ‘not possible’ without manual loading. The manual variant might be the solution of choice for you. Therefore, I will sketch it out later in this post. The first part of this post post is about a trial to achieve this with @EJB annotation only … which failed! But perhaps it will stop some of you to try it out (for nuts) and it’s a great bridge to a solution by a snatch enabling to have circular injection of ‘your own’ beans. I will show you the latter in my next post.
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